Typically in chemical storage and delivery systems, it may be required to be able to inject predictable and some times precise quantities of one fluid into another. Typically, such injection is done by means of a volumetric pump. While such pumps are capable of accurate metering, it is necessary to calibrate and measure the flow rate associated with such a pump in order to establish or verify its flow or pumping rate under existing circumstances since flow rate can vary with the viscosity of the fluid, the depth of the fluid in the tank, the existence of any applied pressure on the surface of the fluid and the different sizes, lengths, and configurations of the suction piping. Accordingly, in view of these changing conditions and the fact that each pump and storage system is somewhat unique, it is desirable to be able to check and calibrate the flow or pumping rate of any fluid storage system where accuracy is important. Also, it is desirable to be able to check the pumping rate at any given moment to be alerted to any pump malfunctioning and blockage in the pump suction or discharge lines.
The prior art has commonly utilized devices such as sight glasses mounted directly on the storage tank to determine changes in liquid level but such devices are difficult to use as the sole means of measuring a small change in level in a large storage tank since the level change may be almost imperceptible until some hours have passed, thus making it impossible to make immediate, meaningful projections of the flow rate. The use of the sight glass to make meaningful estimates of flow is even more complicated when the storage tank is irregular in configuration or shaped in a manner such that a change in level does not produce a proportionate change in volume over the entire depth range of the tank.
It is also known to measure flow rates by utilizing systems where fluid is released from the storage tank and filled into a small calibrated container isolated from the tank and which is branched off the suction line leading to the pump. The rate of removal from the container is carefully measured to obtain a flow rate. However, such systems do not measure the flow rate under the same conditions affecting the storage tank in that the pressure in the container due to depth of fluid is usually quite different from that of the storage tank and the air above the fluid in the container is seldom at the same pressure as that above the fluid in the storage tank; also the effective length and configuration of the suction line between the pump and the container is most often different from that between the pump and the storage tank. Therefore, the net positive suction head (NPSH) available at the pump suction valve is usually not the same during the pumping and calibration cycles which correspondingly affect the flow rates. Most often the pump is stopped before and after the calibration cycle, thus lending uncertainty to the actual pumping flow rates before and after the calibration cycle.
It is also known to measure flow rates from a small calibrated container, normally of a box configuration, which is isolated from the storage tank but which is an integral part of the pump suction system installed at approximately floor level. The fluid level in the container is controlled by float operated control valve installed on the incoming line from the storage tank. The fluid is drawn directly from the calibrated container during both the normal pumping operation and during the calibration cycle. This float box, calibrated container system is normally relatively expensive and requires additional installation area. It is generally limited to lower pumping rates and to unpressurized storage systems. Additional calibration time is usually required to obtain accuracy due to the relatively low height and large cross section of the container. Sedimentation within the calibrated container, and keeping the constantly fluctuating float and control valve operative, may require considerable maintenance effort. A defective float or control valve can readily cause overflow and spillage of expensive chemicals from the container. A separate liquid level indicator, at additional expense, is normally required for the storage tank.
It is, therefore, an object of this invention to provide a flow-rate verification and calibration device and method which is suitable for general use, which is available for immediate use at any moment during the pumping operations for rapid calibrations, which is capable of a high degree of accuracy, which is easy to maintain and which is inexpensive to manufacture. Economy is realized through the utilization of a single liquid level determining device for both the calibrated column and the storage tank. Dual calibration factors may be determined for the device, one factor applicable for the momentary flow-rate determinations utilizing the calibrated column and the other factor applied to determine overall consumption as observed from the liquid level changes in the storage tank.